Conventional burglar alarm devices generally use various types of sensors to detect intrusion of external objects, then determine whether to send out alarm signals through sound or light to avert intrusion or scare intruders. At present, a dual sensing technology has been developed that functions by incorporating a microwave sensor and a passive infrared (PIR) sensor with mating software.
For instance, U.S. Pat. No. 6,188,318 discloses a dual-sensing intrusion detection device for detecting an intruder that comprises a PIR sensor and a microwave sensor. The device comprises PIR processing means and microwave processing means, means for summing the processed PIR signal with the processed microwave signal to generate a summed signal, and means for comparing the summed signal to a sum threshold value to determine if an alarm condition exists. The sum threshold value is selected for optimal discrimination between a human intruder and an animal presence. An additional feature of the intrusion detection device is the generation of a PIR difference signal. This feature allows the device to compensate for the limited bandwidth of the PIR sensor and to be more sensitive to a human intruder. The processing of the sensor signals includes an integration technique that sums the amplitude values of the signal and causes the sum to decay at a slow rate. In addition, the slow decay rate causes the signal to be spread out in time, thereby allowing the signals from both detectors to be above the threshold at the same time.
U.S. Pat. No. 7,679,509 also discloses a Doppler microwave system which is capable of detecting an object range and adjusting the sensitivity of the PIR detector to account for object size and range. Multiple range limited MW stages may be configured for different ranges to determine the general range of the moving object. Based on signal levels present on these MW stages, an approximate object range is determined. The sensitivity of the PIR is then adjusted based on a PIR sensitivity vs. object range function that is optimized to alarm on humans and ignore small animals and insects.